Adhesives have been used for a variety of marking, holding, protecting, sealing and masking purposes. Adhesive tapes generally comprise a backing, or substrate, and an adhesive. Among the types of adhesives used in tapes, are pressure sensitive adhesives and heat-activatable adhesives, with pressure sensitive adhesives being the more common.
Pressure sensitive adhesives are well known to one of ordinary skill in the art to possess certain properties at room temperature including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength. The most commonly used polymers for preparation of pressure sensitive adhesives are natural rubber, synthetic rubbers (e.g., styrene/butadiene copolymers (SBR) and styrene/isoprene/styrene (SIS) block copolymers), various (meth)acrylate (e.g., acrylate and methacrylate) copolymers and silicones. Each of these classes of materials has advantages and disadvantages.
Heat-activatable adhesives are non-tacky at room temperature but become tacky and capable of bonding to a substrate at elevated temperatures. These adhesives usually have a Tg (glass transition temperature) or melting point (Tm) above room temperature. When the temperature is elevated above the Tg or Tm, the storage modulus usually decreases and the adhesive becomes tacky.
A number of siloxane-based pressure sensitive adhesives have been described. A number of these siloxane-based pressure sensitive adhesives contain segmented siloxane copolymers, including silicone polyurea block copolymers and polydiorganosiloxane polyoxamide block copolymers. Silicone polyurea block copolymers are disclosed in, e.g., U.S. Pat. Nos. 5,512,650, 5,214,119, 5,461,134, and 7,153,924 and PCT Publication Nos. WO 96/35458, WO 98/17726, WO 96/34028, WO 96/34030 and WO 97/40103. Polydiorganosiloxane polyoxamide block copolymers are described, for example, in US Patent Publication No. 2007/0148475. These polymeric materials are typically non-adhesive materials, often having release properties, and are formulated with silicate tackifying resins (such as MQ resins) to produce pressure sensitive adhesives.
Additionally, U.S. Pat. No. 5,866,222 (Seth et al.) describes the modification of silicone polyurea release coatings to give non-tacky coatings with higher release values to, for example, block copolymer-based pressure sensitive adhesives, through the use of 1 to 30 weight percent of MQ tackifying resin.